Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $65.34   12.201%   $73.3121   $73.31   $73.30   $73.30  
  Purchase #2 $244.72   10.233%   $269.7622   $269.76   $269.75   $269.80  
  Purchase #3 $134.47   6.873%   $143.7121   $143.71   $143.70   $143.70  
  Purchase #4 $93.58   3.620%   $96.9676   $96.97   $96.95   $97.00  
  Purchase #5 $153.35   9.149%   $167.38   $167.38   $167.40   $167.40  
  Purchase #6 $45.74   3.703%   $47.4338   $47.43   $47.45   $47.40  
  Purchase #7 $155.94   5.814%   $165.0064   $165.01   $165.00   $165.00  
  7 purchase totals = $893.14       $963.5742   $963.57   $963.55   $963.60